The invention relates to a decoding device for decoding a transmitted signal. The invention also relates to smart card systems having such a decoding device.
Decoding devices are used when a signal transmitted on a sub-carrier has to be decoded into a binary code. However, a problem with using them is that the received signal generally differs considerably from the ideal signal. The differences are manifested in noise spikes, changes in pulse length and signal drifts. The causes of the differences lie in the smart card systems, the signal quality of the smart cards and the quality of the analog part. The distance from the smart card to a reading device and the sensitivity of the receiving apparatus also influence the signal form. The faults must be filtered out for error-free decoding.
Conventional decoding devices are based on analog signal processing. Low-pass filters and Schmitt triggers are used to filter out a stable signal. However, those decoding devices are relatively costly for achieving reliable decoding. In addition, all the faults (occurring in the transmitted signal) cannot be detected and/or corrected. Furthermore, those decoders are inflexible if the coding and the transmission system are to be varied.
It is accordingly an object of the invention to provide a decoding device and a smart card having such a decoding device that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, that enable reliable decoding of a signal and that are flexible in application.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a decoding device having a signal-conditioning device that generates an intermediate signal (from an analog input signal) for digital processing and a data register for accepting a time section of the intermediate signal. A bit decoder for converting the time section of the intermediate signal stored in the data register to an output signal having one bit, and a pattern recognition device that works together with the bit decoder are also provided.
In accordance with another feature of the invention, the signal-conditioning device includes a synchronization device having an output for outputting a digital signal. It also includes a sampling device (for sampling the digital signal) having an output for outputting the intermediate signal.
An analog signal is processed in the signal-conditioning device until an intermediate signal enabling digital processing is available at the output. Noise spikes are detected and suppressed, which advantageously takes place during synchronization. In addition, pulse lengths are corrected and a frequency drift of the data stream is detected and compensated for. This is done in the sampling device.
In accordance with a further feature of the invention, the signal-conditioning device includes a fault detector.
In accordance with an added feature of the invention, the signal-conditioning device has a fault corrector.
In accordance with an additional feature of the invention, the pattern recognition device works on a rule basis.
In accordance with yet another feature of the invention, the pattern recognition device has parameters to be changed.
In accordance with yet a further feature of the invention, the parameters of the signal-conditioning device can be changed by software.
With the objects of the invention in view, there is also provided a smart card having such a decoding device including a signal-conditioning device for generating an intermediate signal from an analog input signal for digital processing. The decoding device includes a data register coupled to the signal-conditioning device for storing a time section of the intermediate signal, a bit decoder coupled to the data register for converting the time section of the intermediate signal stored in the data register into an output signal having one bit, and a pattern recognition device coupled to the bit decoder.
In accordance with a concomitant feature of the invention, there is provided a reading device having a decoding device.
Further, the intermediate signal is stored in sections in the data register. The bit decoder decodes the section of the intermediate signal stored in the data register into one or more bits. The bit decoder works with a pattern recognition device for decoding. Thus, even faulty or incompletely transmitted signal sections can be detected. This is one of the advantages, since the costs of signal conditioning and configuration of transmission links can be limited.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a decoding device and a smart card having such a decoding device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.